Once again a matter of preference. I'd pick Justice, but as you can tell by my signature and avatar I am biased towards her, but I'll try to make an objective breakdown.

A TJC/Toromea file's playstyle plays a lot like an advanced rush, so you'll not have a hard time adapting to playing a different concept if you decide to make a refess warriors file.

On the other hand picking Shelby can be the first step on a journey of exploring variety, i.e. Control files, which benefit greatly from the soul skill combination mentioned by Ruki. But keep in mind that going a different path is not as advised at the beginning, unless you completely dislike the current one.

Emana is a niché card, and Millia is pretty outdated, so I'd not consider those.

Basically Justice is a really good card, though you need to get multiple copies of her and you'd need some other cards to go with her. Shelby is a decent SS and can be used immediately, however it's not an SS that's absolutely needed for any file (Generally Shelby is used mostly in falkow files). The choice depends a bit in what you prefer to play and what cards you already have. If you fancy playing refess warriors some day, you might as well pick justice I guess.

"Truly, if there is evil in this world, it lies within the heart of mankind.'